Remote recondenser with intermediate temperature heat sink

Abstract

A recondenser with a primary heat exchanging surface for recondensing boil-off within a cryostat provides a second heat exchanging surface for removing heat leak into the cryostat. The second surface is cooled by the same working fluid that cools the primary surface, but at a temperature intermediate that of the primary surface and associated cooling apparatus which is remote from the cryostat. An intermediate transfer line transfers working fluid from an intermediate portion of the cooling apparatus to the second surface which is in heat exchange relation with a radiation shield of the cryostat but is out of physical contact with the radiation shield. The cooling apparatus includes a mechanical refrigerator which further cools working fluid returned from the second surface through the intermediate transfer line. The intermediate transfer line is preferably positioned in a non-contact helical manner about a final transfer line which carries the working fluid to the primary surface. The two transfer lines form an assembly which is less than about one inch in outer diameter and is removeably positioned in the cryostat. The intermediate transfer line is thermally isolated from the final transfer line within the assembly.

I claim: 
     
       1. A cryogenic recondenser for recondensing cryogen retained in a storage vessel having a radiation shield, the recondenser comprising: cooling means positioned outside of the storage vessel, the cooling means having a mechanical refrigerator and pre-cooling a volume of working gas;   an intermediate transfer line leading from an intermediate portion of the cooling means into the storage vessel;   an end of the intermediate transfer line in the storage vessel being in thermal communication with but out of physical contact with the radiation shield of the storage vessel, partially pre-cooled gas being transferred in the intermediate transfer line from the intermediate portion of the cooling means to the end of the intermediate transfer line and back to the cooling means for further cooling, said transferring being in a manner such that the end of the intermediate transfer line through the partially pre-cooled gas removes heat from the radiation shield; and   a final transfer line removeably leading into the storage vessel from the cooling means, an end of the final transfer line in the storage vessel being in heat exchange relation with boil-off from the cryogen retained in the storage vessel, pre-cooled gas being transferred in the final transfer line from the cooling means to the end of the final transfer line in the storage vessel in a manner which cools and recondenses the boil-off.   
     
     
       2. A cryogenic recondenser as claimed in claim 1 wherein the final transfer line comprises two inner adjacent tubes positioned within an outer tube along axes parallel with a major axis of the outer tube, the pre-cooled gas being transferred from the cooling means to the end of the final transfer line in one inner tube and being transferred back to the cooling means for recycling in the other inner tube, the two inner tubes being in thermal contact with each other along adjacent sides, but insulated from the outer tube. 
     
     
       3. A cryogenic recondenser as claimed in claim 2 wherein the end of the intermediate transfer line is positioned about the two inner tubes in a contact free helical manner within the outer tube and is in physical and thermal contact with a portion of the outer tube positioned in the storage vessel to remove heat from the radiation shield, the portion of the outer tube being in thermal communication with but out of physical contact with the radiation shield. 
     
     
       4. A cryogenic recondenser as claimed in claim 3 wherein the portion of the outer tube is a heat station which is in thermal communication with but out of physical contact with the radiation shield. 
     
     
       5. A cryogenic recondenser as claimed in claim 3 wherein the outer tube has an outer diameter of less than about one inch. 
     
     
       6. A cryogenic recondenser as claimed in claim 2 further comprising: a J-T valve connected to the one inner tube for receiving and expanding the pre-cooled gas; and   a heat exchanger connected to the J-T valve for receiving the expanded pre-cooled gas and passing the same in heat exchange relation with the boil-off such that the boil-off is cooled and recondensed.   
     
     
       7. A cryogenic recondenser as claimed in claim 6 wherein the heat exchanger comprises a first tube coaxially positioned within a second tube, the first tube for receiving the expanded, pre-cooled gas from the J-T valve and passing the same to the second tube in heat exchange relation with the boil-off, the second tube for passing the expanded pre-cooled gas to the other inner tube of the final transfer line; the second tube having an outer surface comprising a plurality of burrs.   
     
     
       8. A cryogenic recondenser as claimed in claim 6 wherein the cooling means includes a second J-T valve. 
     
     
       9. A cryogenic recondenser as claimed in claim 1 wherein the intermediate portion of the cooling means is between a first and second stage of the mechanical refrigerator, and the partially pre-cooled gas is returned to the second stage of the mechanical refrigerator from the end of the intermediate transfer line. 
     
     
       10. A cryogenic recondenser as claimed in claim 1 wherein the intermediate transfer line and the final transfer line are thermally isolated from each other such that working gas being transferred in the intermediate transfer line is kept out of heat exchange relation with that being transferred in the final transfer line. 
     
     
       11. A cryogenic recondenser as claimed in claim 1 wherein the final transfer line has an outer diameter of less than about one inch. 
     
     
       12. A cryogenic recondenser as claimed in claim 1 wherein the volume of working gas is helium. 
     
     
       13. A cryogenic recondenser as claimed in claim 1 wherein the intermediate transfer line carries a full flow of the volume of working gas in series with that of the final transfer line. 
     
     
       14. A cryogenic recondenser for recondensing gas evaporated from liquid cryogen retained in a storage vessel, the vessel having an outer housing, an inner container for liquid cryogen, a transfer tube from the outer housing to the inner container and a radiation shield surrounding the inner container and in thermal contact with the transfer tube, the recondenser comprising: external cooling means including a mechanical refrigerator positioned outside of the storage vessel; and   a transfer line extending from the external cooling means and removeably suspended in the transfer tube, the transfer line comprising:   a final section for transferring incoming cooled refrigerant from the external cooling means to a JT valve in communication with a recondensing heat exchanger and for returning refrigerant from the recondensing heat exchanger to the external cooling means in heat exchange relationship with the incoming refrigerant and   an intermediate section for transferring cooled refrigerant from the external cooling means to a heat station positioned on the transfer line in thermal communication with but out of physical contact with the radiation shield to cool the radiation shield and for returning the refrigerant to the external cooling means out of heat exchange relationship with the incoming cooled refrigerant, the refrigerant of the final and intermediate sections of the transfer line being kept out of heat exchange relationship with each other.   
     
     
       15. A cryogenic recondenser as claimed in claim 14 wherein the transfer line has an outer diameter of less than about one inch. 
     
     
       16. A cryogenic recondenser as claimed in claim 14 wherein the refrigerant is helium. 
     
     
       17. A cryogenic recondenser as claimed in claim 14 wherein the intermediate section transfers a full flow of the refrigerant in series with that transferred by the final section. 
     
     
       18. A cryogenic recondenser as claimed in claim 14 wherein the final section comprises two adjacent tubes, the incoming cooled refrigerant being transferred to the J-T valve in one of the adjacent tubes and the refrigerant returned from the recondensing heat exchanger to the external cooling means in the other adjacent tube, the two adjacent tubes being in thermal contact with each other such that the returned refrigerant is in heat exchange relationship with the incoming refrigerant. 
     
     
       19. A cryogenic recondenser as claimed in claim 18 wherein the intermediate section comprises a tube helically positioned about the two adjacent tubes in a contact free manner and in thermal contact with the heat station on the transfer line to remove heat from the radiation shield. 
     
     
       20. A cryogenic recondenser as claimed in claim 18 wherein the recondensing heat exchanger comprises first and second coaxial tubes, the first tube for receiving refrigerant expanded through the J-T valve and passing the refrigerant to the second tube in heat exchange relation with the gas evaporated from the liquid cryogen retained in the storage vessel, the second tube passing the refrigerant to the other adjacent tube of the final section; the outer of the first and second coaxial tubes having an outer surface with a plurality of burrs.   
     
     
       21. A cryogenic recondenser as claimed in claim 14 wherein the external cooling means comprises a second J-T valve. 
     
     
       22. A cryogenic recondenser for recondensing the gas evaporated from liquid cryogen retained in a storage vessel, the vessel having an outer housing, an inner container for liquid cryogen, a transfer tube from the outer housing to the inner container and a radiation shield surrounding the inner container and in thermal contact with the transfer tube, the recondenser comprising: exterior cooling means including a mechanical refrigerator positioned outside of the storage vessel; and   a transfer line extending from the exterior cooling means and removeably suspended in the transfer tube for transferring cooled refrigerant from the exterior cooling means to a recondensing heat exchanger, the transfer line further comprising a heat station at a mid-portion thereof positioned in the transfer tube and thermally isolated from the recondensing heat exchanger, the heat station being cooled by the refrigerant and in thermal communication with but out of physical contact with the radiation shield to cool the radiation shield.   
     
     
       23. A cryogenic recondenser as claimed in claim 22 wherein the transfer line is less than about one inch in outer diameter. 
     
     
       24. A cryogenic recondenser as claimed in claim 22 wherein the refrigerant is helium. 
     
     
       25. A method of recondensing boil-off from a bath of cryogen retained in a storage vessel, the vessel having an outer housing, an inner container for liquid cryogen, a transfer tube from the outer housing to the inner container and a radiation shield surrounding the inner container and in thermal contact with the transfer tube, the method comprising the steps of: cooling a volume of refrigerant in an external cooling means which is remote from the storage vessel;   transferring the cooled refrigerant in an intermediate section of a transfer line to a heat station position on the transfer line in thermal communication with but out of physical contact with the radiation shield to cool the radiation shield, the transfer line extending from the external cooling means and removably suspended in the transfer tube;   returning the cooled refrigerant through the intermediate section of the transfer line from the heat station to the external cooling means;   transferring incoming cooled refrigerant in a final section of the transfer line from the external cooling means to a JT valve in communication with a recondensing heat exchanger positioned in the inner container;   expanding the cooled refrigerant through the JT valve to form a liquid and gas refrigerant mixture in the recondensing heat exchanger which is in heat exchange relation with the boil-off to cool the boil-off and thereby recondense the boil-off; and   returning the refrigerant from the recondensing heat exchanger to the external cooling means through the final section of the transfer line in heat exchange relationship with the incoming refrigerant, the refrigerant of the final and intermediate sections of the transfer line being kept out of heat exchange relationship with each other.   
     
     
       26. A method as claimed in claim 25 wherein the step of cooling the refrigerant includes passing the refrigerant through a first stage of a mechanical refrigerator of the regenerator-displacer type in the external cooling means. 
     
     
       27. A method as claimed in claim 25 wherein the gas is helium. 
     
     
       28. A method as claimed in claim 25 wherein the intermediate section of the transfer line and the final section of the transfer line are thermally isolated from each other.